Origins of Singlet Fission in an Organic Solar Cell

In this image, an optically excited spin-singlet state (red), which features electron-hole pairs, splits into a pair of spin-triplet states (blue). The individual triplets have equal and opposite center-of-mass momenta – they behave like waves moving in opposite directions along a crystal. The gray and white spheres represent carbon and hydrogen atoms, respectively.

Scientific Achievement

Foundry staff and users have pinpointed the mechanism behind an ultrafast and efficient process that spawns several carriers of electrical charge from a single particle of light in organic solar cells.

Significance and Impact

The discovery will enable the design of materials that are better at harvesting light and lead to gains in solar cell efficiency.

Research Details

Organic solar cells are cheaper and made of materials less toxic than conventional solar cells, but tend to be less efficient.

A process called “singlet fission”, similar to the splitting of atomic nuclei in nuclear fission, rapidly converts sunlight to electrical charges instead of losing it to heat.

The new mechanism explains how singlet fission can occur in just tens of femtoseconds (quadrillionths of a second), before competing processes can steal away the energy.

Calculations performed at the Molecular Foundry and NERSC revealed a close relationship between structural symmetry of the organic cell crystals and energy efficiency.